High-e-beqirency composite set



Nov'. 4. www H LMEJM HIGH FREQUENCY COMPOSITE SET ATTORNEY.

Nov. 4 1924. MWIYM M. s. mmmmwiri HIGH FREQUENCY COMPOSITE SET Filed Jun@ 3. 1919 2 Sheets-Sheet IN I/ EN TOR. HCL Uflz/ BY A iogr" TTORNEY titl Patented Narr; el, llitllllfh MITE 5TM rlpplieeti-on :titled time e?,

To f/ZZ fui/rom 'it may concern.'

Be it known thru' llanotn tl. @moet reeidingg at lieu' l( o rliz, in the count' t csv York and "t, certain, liniprotemente in Coinpoeite tiefe, ot which the toll epecicetion.

'.lhiie invention rela/tee to t"anen'iieeion teme in 'which carrier corrente are en'iployed tor the transenieeion olf eizggnale.

(lne oit the olijecte et thie in vcntion isi; to provide a n'ieaine tor eeiimfratingr into diler4 ent branchee ot "i, conmion trameiieeion cir cuit 'frequencies lying; to either eide ot :i delinilo limit or il'requency eo that low lirequency corrente may be traneoiitted over one branch and high lfroquency corrente tranenii'tted over the otheiix t t'nrther object oil? the invention hae relierence Ato the provision ol" menne whereby a, multiplex earl'ieif eyeteili may he elu'ierpoeed upon an ordinary eignalinp; line, euch ae a telegraph or telephone line, without nereeeitatingl any alteration or reerrengement ol4 the lou7 lrequency epperetue norn'uillyr aseocia/ted with euch e line.

l Stillv iturthcr object ot the invention hee reference to the provision, ol" mezine whereby in a eyeten'x et the cl'ieracter 'just relerred to the carrier trequenciee nniy be eepnmted trom the low 'troqi:enc/iesn which :ire ordinarily need in transenittinp; segnale over the line.) the carrier treououcieo l'loinu' tranen'iittcd over a branch with which :ire associated :1, carrier referring; circuit and a carrier triuiemieeion circuit eo related es to be Substantially conjugate with respect to each other; that ie, eo related that an electro motive :torce in the one circuit will he eubetantielly without ellject upon the other cirenit.

The Several objects it trie invention are accompliehed by connectinm e breneli to an ordinary trenemlegion circuin euch as a, telephone line, at e.V point where it ie desired to Separate the carrier itifequencioe trom the ordinary Signaling trequenciee end .including` in said branch a, broad band tilter, so designed :te to transmit with neo Lgible attenti ation treqiiienciee above the i, per range ot ordinary eignaling` lireipienci and to eub etentially ei ipreee 'troonenciee lyino; below this limit. lluch an ertanojenient will per mit the tranenlieeion of corr'v ,r ce; rent over tile branch but will not permit the traine n sion ol? the low 'frequency cui-rente. In order to prevent the high frequency or ce1n rior corrente tranemitted over the line from passing into that portion et the line beyond the point at which the high frequency branch ie connected, another broad bend lilter ie inserted in the line beyond eaid pointr eeid filter being eo designed :1e to tranfnuit with negligible attenuation tre quenciee lying; below the upper limit olf o1.1u dinary Signaling frequencies and to eubetantially f-iulgipreefs 'frequencies above Seid limi t. By means olf this arrangement, the cari :r lirequencice Superpoeed on. an ordimuy low 'trequency transmission circuit may be taliien ott' at any deeired point and tranemitted over a branch to carrier apparatus Without any rearrangement of the lou7 'trequ ency circuit.

l'n order that the branch circuit above retei-red to, which ie r,eed solely tor the tiene ineeion ot carrier cru-rents, may be eesociated with separate Sending end receivingl circuits, e belencingl transformer end e belancingg1 circuit are provided. ln the balancing; circuit a filter to balance the lilter in the above mentioned carrier branch is provided. rllhe balancing circuit is also provided `with two lziraiichee, in one oit Which a low trequency l'ilter 'tor balencii'igthe low lreqiieney lillter u the main line in sorted, while the other branch includee a network ,tor halencing the main line.

rllhe invention niey now be more liully undereti'xod by reiterence to the followingv dew ecrplion when reed .in connection with the areoinpaiiyiine; drawing', Figure l of which eliowe in Schematic :torni the general ley out oit the terminal carrier efjiuipment superpoeed upon en ordinary transmission line, euch ae n telephone or telegraph line, While 2 and eriow in detail two arrangeu niente ot the high :frequency composite eet, `whereby the cnirier eyetem ie seperated from the ordinary low trequency System.

:tellerring to lFigg. l., ML represente en ordinary tranen'iieeion line, euch ne e telephone line, efiid line terminating` in e termiJ al line lUl including; the usuel composite eet, whereby the telephone circuit may be composited ttor Morse operation, end the usual phantom coil Y and composite ringer @lince the elemente EL Y sind El ere Well known in art they are simply indicated schematically upon the drawing and no further description is deemed necessary.

In order that a` carrier system may be superposed upon the transmission line ML, a carrier branch CB is connected to the main line ML at the junction point of said main line with the terminal line TL, said carrier branch leading to terminal carrier apparatus.v In order to prevent the transmission of the carrier frequencies to the terminal line LT and the low frequency apparatus associated therewith, a broad band filter LF is inserted in the terminal line LT said filter being so designed as to transmit frequencies below the upper limit of telephonie transmission and to substantially suppress frequencies above such limit. In order to prevent the transmission of low frequency currents, such as ordinary telephone or liiorse currents, to the carrier branch CB', a broad and filter HF is inserted in said branch, said filter being so designed as to transmit frequencies lying above the upper limit of ordinary telephonie transmission while suppressing frequencies lying below said limit.

These filters may be of the general type disclosed in United States patents to George A. Campbell, Numbers 1,227,113 and 1,227,- 114e, dated May 22, 1917. As shown in more detail in Figs. 2 and 3, the high frequency filter HF consists of a plurality of sections, each includingr series capacity and shunt inductance, while the low frequency filter LF comprises a plurality of sections, each including series inductance and shunt capacity; The filters, however may be otherwise constructed, the only requirement being that they transmit a band of frequencies having the limits above referred to.

The carrier branch CB is associated with a carrier transmitting circuit TL and a carrier receiving' circuit RL to which the various carrier channels are connected. The circuits T L and RL are associated with the carrier branch CB in such a manner as to be conjugate with respect to each other, that is, carrier oscillations transmitted from TL to CB will be without effect upon RL and vice versa. This result is secured by providing a balanced transformer arrangement 1.0. Yof well known type, and a balancing circuit N.

The details of the balancing circuit N are shown in Fig. 2 and comprise a filter HF to balance the filter HF, and two branches, one including a network MN to balance the main line ML and the other including a low frequency filter LF to balance the filter LF. Tf desired the composite set X may also be balanced by a network XN and the terminal line LT may be balanced by a network TN. In many cases, however, a sufiicient degree of balance may be secured by omitting one or both of the networks TN and XN.

As illustrated in Fig. 2, the carrier branch Gli connected to the main line ML between said line and the composite set X. This connection may, however, be made beyond the composite set as shown in Fig. 3, in which case the correspondingT balancing nelwork XN will be included in the same branch of the balancing circuit as the network MN.

The carrier transmitting and receiving,r circuits TL and RL are associated with a plurality of carrier channels, which will now be described. L1, L. L., and Ll represent low frequency telephone or telegraph lines over which telephonie or other signals arc transmitted. which signals are to be impressed upon carrier currents and simultane ously transmitted over the main line ML. The line L1 is associated with a carrier transmitting circuit TL1 and a carrier receiving circuit RL1 through a balancing transformer arrangement 11 and a balancing network Nv the connection being such that the circuits TL1 and RLl will be conjugate with respect to each other. ln a similar manner, line L., is associated with circuits TL2 and RL., through transfori'ner 12 and network N2: line L., is associated with circuits Tir, and lili, through transformer 1? and network N3; and line Li is associated with circuit-s TL4 andvRL., through transformer 14 and network Ny Each of the transmitting channels TL TL2, TL3 and TL4 is connected to the common transmitting circuit TL while each of the receiving channels R RL., R, and R, is associated with the arrier receiving circuit RL.

In order to supply the carrier currents having different frequencies for each channel, a frequency control system of the general type disclosed in the application of B. lV. Kendall, Serial Number 130,350, filed November 0, 1016, is provided. Tlul fre qnency control system comprises an oscillator FG, which may be of any well known type, such as, for instance, the well known vacuum tube oscillator, said oscillator scrving to generate a basic carrier frequency illustrated, by *ay of example, in the drawA ing as being 5,00() cycles. Tn order to translate the basic .frequency into harmonics for the different channels, an harmonic producer schematically indicated at HP is provided. This harnionic producer may be a vacuum tube arrangement for distorting the waves generated by the oscillator FG so as to produce harmonics in the output circuits of the distorting tube. Harmonic producers of this character are shown and described in the above mentioned application of B. W. Kendall. as well as in a patent to B. 1V. Kendall, No. 1,446,752, dated Feb. 27, 1923. The harmonics produced by the harmonic producer HP, which may be for example of 10,000. 15.000, 20,000 and 25,000 cycles. are filtered out and separately transmitted to the il. l. alle l eh an nele tln'o negli i 2, UF3 and GF4. 'Ther-vteringl de ifieee may he liu'ead hand lil the type deel eed in the ahoife Iiientiound patente of `George lli. tlarnphell or may he Simple tuned eilenite of anyY Well known type. The fumlaniental frequency here illustrated ae 5,000 e'ir'clee` may lie tranefslnitted through a Similar filtering;l arrangeur, FF te an amplifier FA. 'lllie amplifier Fil. may be of l i3 known type euch as, for in stanca, a ,fzfujaunn tube amplifier. lhe arnplified fundaniental frecnmey may lie then paseed through. another filter fl and iinpressed 'upon the traneinittr e eajfrier eirfiaiit Tl.;u The harmonies need ae carrie.' frequencies after lieing filtered hy :menne of the filiere CFI, CFE, ete., may he inipreeeed nnen. carrier amplifiers (ML, CA2, C ll; and Cilly Theee ampliliere .may be eiinilar to the an1- plilier Fill already referred te Each of the traneinilatine; cl annele flllw TLT ete, is provided with. a. modulating arrangement echeInat'ically ilh et 'ated at fl, M29 M1; and NL. rlliil: .modrilatingl arrangenient may he of any deeired charziietei.' hut ie 'pre'leral'ilj@T a vaetunn tnlee ar angen'u-nitj eneh ae .ie illustrated in the patent to ll, 'Wl llendall, Ne. `l,4l50.700, dated .linie lll, w23, or in Athe patent to John lt. Carnon, llo litt-3,207, dated lune lll, 195210.

Each of the receivingI ehanneleI "S provided with a deu'lodnlator or detecten, euch as; lll, D2, D.; and D1, These demodulating or detecting;l arrangements may be of any Well known type, lont are preferably of the type illustrated and deecrihed in the latent of J. R. Carson, l'l'innher le; 41:3?300, dated lune 15, 1920. The detecting' o1' deinmlulatingI arraneen'ient of the eaid patent of ml. @an son employe th 1( sse-walled hemodyne method of deter/tine'g therelii)7 necessitating' that the earrier frequency/' of that particular elnumel he einiiplied te the deniodulatn wrang-re nientv A ccordingly the carrier ilrequeney of each channel after heine` amplified hf( the carrier ainplilierey CAM CA2, etc., is; Supplied in parallel to the inodnlatinel arrangement of the tran emitting; channel an d. the deinodnlat ing* ai' 'angelnent of the correeponding receiving channel..

The carrier oscillatione impress-sed 'upon the niodulator, for instance lll/lVU are niednlated hy means of the low fiequencyT eigrnal Waves transmitted from the len7 frequently line, Ieucli ae line L1, to the :arrier ehannel TLl, and are then filtered. and ampli lied. For this purpose broad hand filtert' '.lFw

TF2, TF3 and rlF,1 are provided in Vthe eut put eirenite of the rnfmlulatore lilly lli/l2, lele; and lill. These filters niet7 he of the type disclosed in 'the patente to Caniphell ahoiife referred te and each filter elienld he capable of tranen'nttanp,` a band of frequeneiee whoee Width is equal to the range of freqtie-meleeJ tall Wal ifi low fretgueturi/ l l e n enlieue trinenlw i, the filter ild Y leehrned ae te tranenjiii a hand equal te t telepho renee te the emfhinie i e fredii lying; Witlunit thie ianije. The aetn '.f1qiiea'czieF-1, ti.y emitted hy i;

filter ef each channel will he dillc nt iV f each channel. Lillie filter of the eliannel lll@ tranenfitting a l'and of fredneneiee in the vrlierliood of 9,5?000 e'if'clee, the l er chanel traneinittiingi; a hand in the rioinitiY of lllltlit) cycles? eten 'the modulated carrier eeellatione traneiniftte l threeell i the filters i rlil J1 Y rlllieee ain- Je of am),T well known type het ting' elnmnelst are preferahljyf 'wicnnin tuhe anujilillere. ln orner to further liner ieee the eeleetivity, lil ter lFl, TF2', lflf and lF/ may he @ne vided in the output elreinte of the aini'wlIfieir-t rlhe :level-afl en rrif "rc-enemies; are n'iodnlated in amerdance with the low frequency ein nah; t'anfsin ed, ever the lin Yai lll, lllim la: and

fr, and after heine' filtered and ae'iplited are eine;ltaneeiesly inipreaeed unen the co neon carrier tramunitting; eii'cnit 'Vla the funda-- mental frequency here illuetrated ae heine; :f 57000 eye-lee, heine; at the traine time iiniu'eeeed upon the eon'nnon eii'cuit. 'lheae nudtiple frequencies; are then. tra iienritted te the tranella-nini. l0 and ever the earrieif branch @ll tothe main line lli/lli. tlwiue' lo the halaneingr arra ngreznent of the tranf-tfm'ui1- er l0 and the networll; lll, the reaetion. of these freqneneiee on the @minnen receiving; circuit lll; im@ reduced to eiii'nill. in 'oportionn and ,if a en" ,cient d ,ggjree ef balance is pre- 'vided may he rendered negligible The louT frequency filter llF linfeifente the high fre fluency carrier oeeillatione from heine' traue" niitted to the lerinnal line 'llin lu eaeh el the i'eceiviie eliannela l lll@im ete) a hioad hand filter ie nnlerled en i' arrange tic/allay7 indipreneed through the transformer il the common receiving?,` eire Y Y lated currents eorreeponding; in equenci' to the diflenfeiit channels are filtered ont leT in'ieane of the filter-.eJ llll, ltFZ, el and inipreeeed nnen the deinednlatore DH l'lw etc. llnrnodnlated carrier freqxunicies are at the naine tiine in'linfeeed open `the deinedulatore from lthe centrol :irent alreadw de eci'ihed so than the lcw freeuiener nal Wai/e, .in accordance with 'ufliieli Athe liigJh 'lll l l (l lllll frequency carrier Waves Were modulated appear in the output circuits of the demodir laters.

In order to amplify these low frequency Waves, low frequency an'iplifiers RAM RAZ, RA. and RAl are provided in the several receiving channels. These amplifiers may be of any Well known type but are preferably vacuum tube amplifiers. In order to purify the low frequency currents from any high frequency components, low frequency lilters, such as RF1', RFZ, RF3 and RF1 are provided in the output circuits of the amplifiers. These filters may be of the saine character as the lovv frequency filter LF in the terminal line LT and are of the general type disclosed in the patents to Campbell above referred to. The amplified low frequency signal Waves from the several receiving channels are then impressed through the transformers 11, 12, 13 and 14 upon the respective low frequency lines Ll L2, L,s and L4.

It will be remembered that in connection with the production of the various carrier frequencies, a fundamental frequency of some desired value, such as 5,000 cycles, for example, was generated and transmitted y through the filters FF, and FF and the amplifier FA to the common transmitting circuit TL. This fundamental frequency was then transmitted together with various modulated carrier frequencies through the transformer arrangement 10 and the high frequency lilter HF to the main line ML. At a distant point in the main line the various carrier frequencies may be separated from the loW frequency signaling currents, such as telephone currents, by means of -a high frequency composite set similar to that already described and comprising high fre quency and low frequency filters similar to the filters HF and LF. The carrier frequencies may then be impressed upon terminal carrier apparatus similar to that shown in Fig. 1. The terminal carrier apparatus may differ, however, from that shown in Fig. 1 With respect to the production of the carrier frequencies. In order to illustrate the manner in which the system Will be modified at the distant station in this respect, the apparatus of Fig. 1 has been shown With a circuit 21 leading from the common receiving circuit RL to a harmonic producer (not shown). The filtering arrangement, such as a tuned circuit FR, is included in the circuit 21 to filter outl the fundamental frequency of 5,000 cycles transmit-ted over the line. This frequency is then impressed by means of the circuit 21 upon an harmonic reproducer which will be in general similar to the harmonic producer HP and the general principle of this arrangement is described in the patent of B. W.- Kendall, Number 1,446,752, already re ferred to. The general arrangement where by the harmonic reproducer is associated With the rcceiif'ing circuit shown and de scribed in the application of ll. W, Kendall, Serial Number 130,350, tiled November 9, 1916, to which reference has already been made. It is suflicient for the lmrposes of this application to state that the harmonic reproducer functions to produce harmonics of the basic frequei'icy in a manner similar to the harmonic producer HP already described, the several harmonics being filtered ont, amplilied to a desired valnc and then impressed upon the modulating and demodulating apparatus of the terminal system.

The high frequency composite set comprising the present invention is independent of the nature of the terminal carrier apparatus which has been illustrated and described for purposes of illustration and ma) be used at any point where it is desired to separate the carrier frequencies from the low frequency signal currents which are normally transmitted over the line. This per-- mits of any special treatn'ient which ma y be desired for either the high frequency cal'- rier currents or the low frequency signal currents at any point along the line and enables the superposition of a carrier system upon an ordinary transmission circuit with out any modification of the latter, the entire apparatus being associated with the terminal carrier system so that it can be applied to a line or disconnected therefrom Without materially affecting its transmission properties with respect to low frequenca` currents.

lVhile the invention has been disclosed as embodied in certain circuit arrangements which are deemed to be desirable from a practical standpoint, it will be obvious that the general principles thereof may be embodied .in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the iliollowing claims.

What is claimed is 1. In a transmission system, a main transmission line adapted to transmit both low frequency currents of an order lower than the upper limiting frequency employed in ordinary telephonie transmission and high frequency currents having frequencies of the order used in carrier transmission. branches leading from said line` one branch being adapted to transmit said low frequency enrrents and the other branch being adapted to transmit said carrier frequencies` means in the former branch to substantially exclude arrier frequencies while transmitting with substantially uniform attenuation a range of said low frequency currents, and means in the latter branch to substantially exclude said low frequencies While transmitting with sublll) CFE

iis-rarer stantially uniform attenuation a range of carrier frequencies.

2. ln a. tra emission system, a main. transu missionv line adapted to transmit both .low frequency currents of an ord r lower than the upper limiting frequency employed in ordinary telephonie transmission and high frequency currents having frequencies of the order used in carrier transmission, bianche leading from said line, one branch being adapted to transmit said low frequency currents and. the other branch being,- adapted to transmit said carrier frequencir-is, a filter in the former branch to substantially esclude carrier frequei'icies while transmitting,` with substantially nnilorm atteiiuation a range of said low frequency currents, and a bread band filter in the latter branch so arranged and. constructed as to transmit with substantially uniform attei'iuation a range of carrier 'frequencies and substantially include said low frequencies.

tl. lin a transmission system, a main transn mission line adapted to transmit both low frequency currents of an order lower than. the upper limiting frequency employed in ordinary telephonie transmission, and high frequency curren having; frequencies of the `order used in carrieiI transmission, branches leading from said line, one branch being,` adapted to transmit said. low frequency currents and the other branch lar-zing adapted to transmit said carrier frequencies, means in the former branch adapted to substantially srqiipii'ess currents having frequencies above the upper lin'iits of ordinary telephone tiansn mission. 'While transinitt'ii152iv with substanA tially uniform. attenuation a range of frequencies corresponding to the ordiinufy telephone range, and means .in the latter branch to substantially suppress currents having` frequencies below the upper limits of ordinary 'telephonie transmission while transmitting with substantially uniform attenuation a range of carrier frequencies.

l. In a transmission system, a main trans mission line adapted to transmit both low frequency currents ot an order lower than the upper limitingr :frequency employed in ordinary telephonie transmission, and high fra quency currents having` frequeificies of the order used in carrierl transmission, branches leading' from said line, one branch being :ulapted to t ansmit said low frequency currents and the other branch. being` adapted to transmit said carrier frequencies, a broad band filter in the former branch so constructed and arranged to transmit with substantially 'uniform attenuation currents having; a range of frequencies below the upper limits of ordinary telephonie transmisi sion and substantially suppress currents having; frequencies above said limit, and a broad band filter in the latter branch so con- Struoted and arranged as 'to tiaiisinit with substantially uniform attenuation currents having, a range of frequencies above the npum per limits of ordinary telephonie transin's sion and substantially suppress currents hait iup; frequencies below said limit.

ln a transmission system, a telephone line normally adapted to transmit currents of the order used in ordinary telephonie transmission, low frequency terminal ap paratius for said line adapted to transmit ordinary telephone currents, and means to superpose a plurality of carrier transmission channels on said line comprising a branch connected to said line between the line and said terminal apparatus, said branch leading to terminal carrier apparatus, means in said branch to substantially suppress the transmission ef ordinary telephonie frequency currents thereoyer while transmittingl with substantially un.'I rin attenuation a range of carrier frequencies, and means interposed between said terminal apparatus and the junction point between said branch and the line to substantially prevent the transmisu sion of carrier frequencies to said. terminal apparatus while transmitting with substantially uniform attenuation a range of fre quencies correspondingv to the ordinary tele phone range.

G. lin a transmission system, a telephone line normally adapted to transmit currents of the order used in ordinary telephonie laraiisinissioin low frequency terminal appa ratus for said line adapted to transmit ordinary telephone currents, and means te superpose a plurality of carrier transmission channels on said line comprising` a branch. connected to said line between the line and said terminal apparatus, said. branch leading to terininal carrier apparatus, a broad band filter in said branch so constructed and arranged as to transmit with substantially uniform attenuation frequencies above the upper limit of ordinary telephonie transmission and substantially suppress frequencies below said limit, and a broad band filter interposed between said terminal apparatus and the junction point of said. branch and the line, said filter being.- so constructed and arranged as to transmit with substantially uniform attenuation frequencies below the upper limit of ordinary telephonie trans mission and substantially suppress frequencies above said limit.

i. ln a transmission system, a telephone line normally adapted to transmit currents of the Iorder used in ordinary telephonie transmission, and means to superpose a plurality of carrier transmission channels on a section of said transmission line, said means connnfising a branch connected to said line at one end of the section upon which the carrier system is to be supcrposed, said branch leadiiig,` to carrier apparatus, means in said branch. to substantially suppress the Uli transmission of low frequency currents thereover While transmitting with substantially uniform attenuation a range of ca-rrier frequencies, `and means in the line external vto the section upon which the carrier .System is to be superposed to substantially suppress the transmission of carrier 'frequenc'ies While transmitting with substant'ially` uniform attenuation a range of frev`quencies corresponding to the ordinary telephone range.

8. In a transmission system, a telephone fline normally 'adapted to transmit currents of the order used in ordinary 'telephonie to be superposed, said branch leading to carrier apparatus, 'a broad band filter in said branch so constructed and arranged as to transmit With substantially uniform attenuation frequencies above the upper limit of yordinary Vtelephonie transmission and substantially suppress frequencies below said limit, and a broad band lfilter in the line external to the section upon which the carrier .system is superposed, said filter being so constructed and arranged as to transmit with lsubstantially uniform attenuation frequencies below the upper Ilimit of ordinary telephonie transmission and substantially suppress Ifrequencies above saidliniit.

9. In a'tran'smis'sion system, a main transj'mission' line adapted to transmit both lou7 "frequency 'currents and'high frequency curre'nts'havingfrequencies of the order used in carrier transmission, branches leading from saidline,'one branch being adapted to transmitloW frequency currents and the other "branch being 'adapted to transmit carrier frequencies, inea-ns in said first mentioned rvbranch to substantially exclude carrier `frequencies and means inv said second branch to s'ubs'tantially eXclude loW frequencies, a carrier 'transmitting circuit andra carrier recei'vingcircuit, means to associate said cir- `cuits with said second mentioned branch comprising 'a transformer and a balancing circuitso arranged that said carrier circuits will'be substantially conjugate with respect to each other, said balancing circuit includii'ig'means to'balance said means to exclude low frequency, said rbalancing circuit also being provided With two branches, one

branch including means to balance the means 'to exclude carrier frequencies from .the low frequency branch of the main transli'nission'line,"and the other branch including means to balance the main'transinission line.

` l0. yIn a transmission system, a main "transmission line adapted to transmit both 'lowffrequency currents Vand high frequency currents having frequencies of the order used in carrier transmission.y branches leading from said line, one branch being adapted to transmit loir frequency currents :ind the other branch being adapted to transmit carrier frequencies, means in said vfirst mentioned branch to substantially exclude carrier iirequencies and a broad band tilter in said second branch so arranged and constructed :is to transmit carrier frequencies and substantially exclude low frequencies, a carrier transmitting circuit und a carrier receiving circuit, means to associate said circuits with said second mentioned branch comprising a transformer und a balancing circuit so arranged that said carrier circuits will be substantially conjugate with respect to each other, said balancing circuit including means to balance said broiid bund filter, said balancing circuiti also being provided witli two branches, one branch including means to balance the means to exclude carrier frequencies from the low frequency branch of the main transmission line, :ind the other'branch including means to balance the main transmission line.

li. In a transmission system, a main transmission line adapted to transmit both low frequency currents and high frequency currents having frequencies of the order used in carrier transmission, branches lend-- ing from said line. one brauch being adapted to transmit low frequency currents and the other branch being adapted to transmit carrier frequencies, means in the former branch adapted to substantially suppress currents having frequencies above the upper limits of ordinary telephonie transmission, and means iii the latter branch to substantially suppress currents having frequencies below the upper limits of ordinary telephonie transmission, a carrier traiifsmitting circuit and a carrier receiving circuit. means to associate said circuit with said second mentioned branch comprising :i transformer and a balancing circuit so arranged that said carrier circuits will be substantially conjugate 'with respect; to cach other` said balancing circuit including means to balance said means to siqipress currents below the upper 1iimits of telt-phouir transmission, said balancing circuit also being pro-A vided with tivo branches.` one brauch ineluding' means for balancing press currents above the upper limits of telephonie transniission,y and the other branch including means to balance the main transmission line.

l2. In a transmission system, :i main transmission line adapted to transmit both loiv frequency currents and high frequency currents having frequenci; of the order used iii carrier transmission. branches leading from said line, one branch being adapt,- ed to transmit low frequency currents und iid means` to suptoo itt?

llt)

Lsienei m ble range to prevent the transmission to said branch of audible carrier frequencies transi'nitted over said main line.

23. lin a transmission system, a main. transmission line, branches leadingl from said line, one branch being adapted to transmit loii7 frequency signaling' currents of an order lower than the upper limiting frequency used in ordinary telephonie transmission and the other branch beingl adapted to transmit alternating` carrier currents seine of which may bc audiblea means in the former branch to substantially exclude said carrier irequen cies While transmitting with substantially uniform attenuation a range of signaling frequencies of an order lower than the upper limitiiuq` frequency used in ordinary telcphonic transmission, said means having` an upper cut-off point Within the audible range to exclude audible carrier frequencies, and means in the latter branch to substantially exclude signaling frequencies of an order lower than the upper liiniting1 frequency used in ordinary telephonie transmission f VWhile transmitting` with substanl ially uniform attenuation a range of carrier frequencies said .last mentioned means havingI a lower cut-ofi point Within the audible limit to permit the transmission of audible carrier currents above said limit.

2li. lin a transmission system, a. main trans mission line, branches leading from said line, one branch being adapted to transmit low frequency signaling currents of an order lower than the upper limiting` frequency used in ordinary telephonie transmission and the other b anch being adapted to transmit alternating,1 carrier currents some of which may be audible, a broad band lilter in the former b "anch to substantially exclude said carrier frequencies while transmitting With substantially uniform attenuation a range of signaling frequencies of an order lower than the upper limitingl frequency used in ordinary telephonie t xansmission, said filter hay ingl an upper cut-off point Within. the audible limit to exclude audible carrier frequeir cies, and a broad band filter in the latter branch to substantially exclude sign aling frequencies of an, order lower than the up per limiting` frequency used in ordinary telephonie transmission While transmittingl With substantially uniform attenuation a range of carrier frequencies7 said last mentioned filter having a lower cut-off point Withinv the audible limit to permit the transmission of audible carrier currents above said limit0 lin testimony whereof9 l have signed my name to this specification this second day of June, 1919.

KlOl 

